As examples of a technique for performing signal processing by controlling the phase component of a signal, patent literature 1 and non-patent literature 1 disclose noise suppression techniques which pay attention to a phase spectrum. In patent literature 1 and non-patent literature 1, a magnitude spectrum pertaining to noise is suppressed, and at the same time, the phase spectrum is shifted by a random value of up to π/4. Shifting the phase spectrum at random implements suppression of noise which cannot be suppressed by only attenuation of the noise spectrum.